In the manufacture of molded products, particularly those made of rubber or plastics, the purity and properties of the working area interior surfaces of the die molds are extremely important. They influence the mold filling and especially the soiling of the mold. Measures can be taken in creation of the mold and with the product material used to retain a high purity during the manufacturing process. In addition, auxiliary substances are applied to the working area interior surfaces of the die molds. Thus, parting compounds, for example, are applied by hand to the interior surface of the mold with the help of cleaning cloths, by spraying or the like. It is a disadvantage here that the auxiliary substance is distributed unevenly over the die mold surface. Application of the auxiliary substance depends on the operating personnel and is not clearly reproducible. It is also a disadvantage that an unjustifiably long period of time is required to apply the auxiliary substance.
The object of the present invention is to remedy this situation and provide a method of applying auxiliary substances to the interior surfaces of die molds with which the greatest possible accuracy can be achieved in applying the auxiliary substance and which can be carried out inexpensively in the shortest possible amount of time. This method should contribute toward good mold filling and preventing soiling of the mold to the greatest extent. This should increase the useful lifetime of the mold.
This object is achieved with a method of applying surface-modifying auxiliary substances to the working area interior surfaces of die molds for producing molded products, in particular made of rubber or plastics according to the present invention by supplying the auxiliary substance in the form of a gas or vapor to the interior surfaces of the die mold which is integrated into the processing machine, and the gas or vapor is condensed there. It becomes superfluous to spray the auxiliary substance or apply it with wiping cloths or the like. The gas or vapor form of the auxiliary substance is preferably produced in vacuo. Even a partial vacuum can produce vaporized auxiliary substance. It can then be supplied to the interior surfaces of the die molds and condensed there.
An air flow can contribute toward a rapid and uniform distribution of the vaporized auxiliary substance onto the interior surfaces of the die molds. This flow can be achieved either by natural or forced flow.
One effective technique for promoting the condensation process is to increase the pressure. Controlled condensation on the mold surfaces can be achieved or supported in this way.
The auxiliary substance to be used is to be coordinated with the individual application. The auxiliary substance is selected according to the type of mold, the product to be molded and in particular the temperature to be used. It is preferably accommodated in a heatable depot which communicates with the opened die mold. It can be removed from the depot in portions. In the depot itself, the auxiliary substance may be in solid, liquid or gaseous form. Thus, the auxiliary substance may also be introduced into the depot in individual portions, e.g., in tablet form.
Depending on the product to be produced, the auxiliary substance is selected so that it is deposited on the interior surfaces of the die mold in liquid and/or solid form. For deposition in solid form, it is also possible to work with substances that sublime.
The thickness of the layer deposited on the interior surfaces can be predetermined. For example, it can be controlled by the duration of the condensation phase. With an appropriate adjustment of the individual process steps, extremely thin layers can be achieved.
It is possible with this method to apply a defined layer of the auxiliary substance to the mold before each mold filling operation. However, it is also possible to apply the layer after several mold filling operations in predetermined cycles. Finally, different auxiliary substances can be used with the individual cycles. The latter is readily possible by replacing the auxiliary substance in the depot.
The device for carrying out this method includes a vacuum system for generating the vacuum in the die mold and a depot for the auxiliary substance communicating with it. A very simple option is achieved when the vacuum system is integrated into the molding installation, with the vacuum chamber enclosing the die mold in an airtight manner.